Department of Surgery, Saga University Faculty of Medicine, Saga, Japan.
Am J Pathol. 2011 Feb;178(2):515-24. doi: 10.1016/j.ajpath.2010.10.010.
The hypoxic marker carbonic anhydrase (CA) IX has been recognized as a tumor-associated protein and is essential for cancer development. However, because CA IX expression does not always correlate with hypoxia, its regulatory mechanism remains unclear. The objective of the present study was to clarify the role and regulation of CA IX expression in gastric cancer. The immunohistochemical expression of CA IX and hypoxia-inducible factor-1α was assessed in 77 patients with gastric cancer. A methylation-sensitive restriction enzyme method was used to quantify site-specific methylation at -74 bp in the CA9 promoter in tissue from patients with gastric cancer and in corresponding normal tissue. CA9 expression in cell lines was strongly dependent on methylation status but not hypoxic stimuli. In tissue from patients with gastric cancer, the quantity of methylation was significantly correlated with the protein expression (P = 0.003). Moreover, the methylation value was significantly lower in intestinal-type compared with diffuse-type cancer (P = 0.003). Compared with normal mucosa, intestinal-type cancer demonstrated significant hypomethylation, whereas diffuse-type cancer exhibited hypermethylation. In conclusion, expression of CA IX in gastric cancer is predominantly regulated by methylation of a single CpG rather than by hypoxia. Furthermore, epigenetic alterations in CA9 differ between the intestinal and diffuse types of gastric cancer.
缺氧标志物碳酸酐酶（CA）IX 已被认为是一种肿瘤相关蛋白，对癌症的发展至关重要。然而，由于 CA IX 的表达并不总是与缺氧相关，其调控机制尚不清楚。本研究的目的是阐明 CA IX 在胃癌中的表达作用及其调控机制。对 77 例胃癌患者的 CA IX 和缺氧诱导因子-1α 的免疫组织化学表达进行了评估。采用甲基化敏感的限制性内切酶方法，对胃癌患者组织和相应正常组织中 CA9 启动子-74 bp 处的特定位点甲基化进行了定量分析。CA9 表达在细胞系中强烈依赖于甲基化状态，而不依赖于缺氧刺激。在胃癌患者的组织中，蛋白表达与甲基化数量呈显著相关性（P = 0.003）。此外，肠型胃癌的甲基化值明显低于弥漫型胃癌（P = 0.003）。与正常黏膜相比，肠型胃癌表现出明显的低甲基化，而弥漫型胃癌则表现出高甲基化。总之，胃癌中 CA IX 的表达主要受单个 CpG 甲基化的调控，而不是缺氧。此外，CA9 的表观遗传学改变在肠型和弥漫型胃癌中存在差异。
